Good day!
I have read your project tasks, fully understand your needs, and ready to take on this project. I propose you to implement OpenVPN server inside VOIP server. It's cost effective and cross-platform solution.
I'll be grateful to you for attention and ready to discuss about your project as soon as possible.
I have a lot of experience of system administration Linux / Windows-servers and infrastructure products (Microsoft, Cisco, Fortinet etc.).
Thank you!
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About me
About 7 years I worked as system administrator at a company that provides SaaS-service from Microsoft and Linux/Windows VPS-service. Part of my job is related to the migration of customer services "in the cloud". I also have extensive experience in the installation and support VOIP-based systems (Cisco, Avaya, Asterisk, Freeswitch, etc).